The present invention relates to a semiconductor power module with a power semiconductor device, such as an insulated gate bipolar transistor (hereinafter, referred to as IGBT), mounted thereon, and to a power inverter with the semiconductor power module, and to a method of manufacturing the semiconductor power module.
In the semiconductor power modules for use in the power inverter mounted on electric vehicles, hybrid vehicles, etc., it is required to cool down the modules effectively since their heat value is large, and a liquid cooling is therefore effective as their cooling means. In the liquid cooling, radiation fins are normally adhered on the semiconductor power module via a thermal conduction grease, for example, and the radiation fins are immersed in a flow path of a coolant water. However, the thermal conduction grease has a drawback of such that its heat transfer resistance is high compared with metals.
In contrast, for a purpose of acquiring a higher cooling capacity, JP-A-2007-295765 and JP-A-2005-191502 have been known as a direct cooling-semiconductor power module in which a heat is transferred to a cooling unit without through the thermal conduction grease.
According to the direct cooling-semiconductor power module, the power semiconductor device is directly mounted on the upper surface of heat sink via an insulated layer, and the radiation fins are formed on the lower surface of the heat sink. In this case, this configuration is that an opening portion of an upper surface of a coolant water flow path is closed by a lower surface of heat sink. Therefore, the lower surface of heat sink is directly contacted to the coolant water to improve a cooling efficiency of the heat sink.
In this case, materials of the heat sink are generally of composite materials (SiC, W, Mo, Si, Ni—Fe, etc.) of a low thermal expansibility typified by Al—SiC, and high thermally-conducting materials (Cu, Al) etc. However, there is a problem that the composite materials have 150 to 300 W/mK in coefficient of thermal conductivity, which is lower than that of pure copper (Cu), and are high cost since the manufacturing process is complicated.
In consequence, the JP-A-2007-295765 has disclosed an example using an alloy for the heat sink, which contains copper (Cu), as a chief component, and other materials having inexpensive and good heat conductivity. However, in the case of JP-A-2007-295765, the configuration is that the radiation fins are brazed to the base of heat sink. Therefore, the cooling capacity of the radiation fins should be descended by causing the heat transfer resistance at the brazed portion, compared with the radiation fins which are integrally molded with the pure copper as a base material, for example.
JP-A-2002-18538 has disclosed a technique in which the fins are pressed into the base of heat sink, as a joining method. However, a clearance gap is easily appeared at the joined portion since the base is not integrally molded with the fins, therefore, there is a problem that the cooling capacity is descended by causing the clearance gap.
As for method of integrally molding the base and fins of the heat sink, JP-A-2005-26255 has disclosed a method for a press molding of a copper powder. JP-A-9-3510 has disclosed a method for an injection molding using a binder for joining the copper powder. However, in the case of those methods, the coefficient of thermal conductivity becomes lower than that of a pure copper plate material since the heat sink is molded from the copper powder. Further, there is a problem to cause a void.
As for the method of integrally molding the base and fins of the heat sink, a cutting work method and a forging work method have also been known as disclosed in JP-A-6-224335. These above-mentioned methods are excellent in the sense that high cooling capacity can be obtained in use as a heat sink. However, the cutting work method is unsuitable for commercial production. In also the case of the forging work method, it is difficult to form pin fins (pin type fin) uniformly on an entire copper plate which is sufficiently large as the base of heat sink to be used for the semiconductor power module. Such above-mentioned technical problems have not been adopted so far, and a solution has not been proposed at present.